Role of Climate, Culture, and Waterways in Shaping the Hominin Population Dynamics

Past climate change and cultural evolution played significant roles in the migration of archaic humans into new geographic areas, contributing to the diversification of the genus Homo. The Mid-Pleistocene period was a critical time when Homo heidelbergensis evolved in Africa and migrated to Eurasia, likely leading to the emergence of new human species, including Homo neanderthalensis and Denisovans. The present study investigates how past climate, rivers, and cultural changes affected possible hominin migration routes to northwest Africa and Eurasia, as well as the timing of their arrival. To identify migration pathways across Africa and Eurasia, we conducted an ensemble of sensitivity experiments using a realistic climate-forced agent-based model (ABM) with varying cultural levels and with coastal and riverine routes enabled or disabled. In the absence of coastal and riverine activation and low cultural levels, the hominin population remains confined to southern and eastern Africa. However, with higher cultural evolution, they could reach north-west Africa via the western Saharan route.

The ABM simulations with river and coastal amplification show that the hominin populations migrated to north-eastern Africa via the Nile route at low cultural levels. However, with increased levels of culture, they could reach north-western Africa through the Nile-Mediterranean coastal route, and the north-western African population shows intermittent interaction with the west-central population. Also, over a short period, they dispersed into Eurasia via the Levant and migrated into Europe. Thus, coastal and riverine amplification helped the hominin reach north-western Africa and Europe with relatively low cultural values at the beginning of the middle Pleistocene period, which closely matches the Homo heidelbergensis archaeological record. Additional analysis of our simulations reveals that the precessional cycle played a dominant role in controlling the hominin migration through the corridors. At the same time, population density in African population hotspot regions was controlled by changes in atmospheric CO2 concentration. The phylogenetic analysis of the individual virtual agents' DNA shows distinct branches for the north-west, central, and south-east African populations. Since low-frequency climate cycles isolate and reconnect north-west and central African populations with east and south African populations, they contribute to the dynamics of genetic diversity.